Referring to FIG. 1, a running track disclosed in Russian Patent No. 961,712 and issued to Morozov comprises an endless rubberized bearing belt (B1) mounted on pulleys (P) and a support deck (D) under the upper branch of the bearing belt (B1). An inner endless belt (B2) is rounded freely on the support deck (D) and is made of a material which has antifriction properties with respect to the surface of the support deck (D). The running track of Morozov is not suited for use as a treadmill apparatus by people with uncoordinated feet movement, such as small children, physically handicapped people and old people, since the left and right feet of the user both tread a single, wide bearing belt (B1) at the same time. Thus, a twisting moment (T1), (T2) applied by either the left foot (L) or the right foot (R) when treading the left-side or right-side parts of the bearing belt (B1) may influence smooth running of the latter relative to the inner endless belt (B2).
U.S. Pat. No. 4,204,673 to Speer, Sr., discloses a dual-tread exerciser which uses a large plurality of parallel roller bearings to support the treads. Such roller bearings have proven to be uncomfortable on the feet and are not suited for use by children and others having sensitive feet or who desire a more comfortable feel, particularly when exercising barefoot. Two motors are required to motorize the device of Speer, Sr.